Summary: Immune Basis and Clinical Implications of Threshold-Based Phenotypes of Peanut Allergy Peanut allergy (PA) is common, affecting 2-5% of school-age children in the US. The characteristics of PA vary widely among individuals, with some reacting to 1/100th of a peanut and others not having symptoms until they have ingested many peanuts. Symptoms can vary from mild rashes to fatal anaphylaxis. There is no FDA- approved treatment, and all patients with PA are managed with strict allergen avoidance. Most research on PA has focused on those with the most exquisite sensitivity to peanut. Immunotherapy trials commonly exclude subjects with a threshold dose over 1/3 of a peanut (100mg). However, most individuals with PA have higher thresholds of reaction and are excluded from current research approaches. We hypothesize that the natural heterogeneity of PA is a valuable opportunity for investigation. We have shown that milk or egg allergic individuals with tolerance to baked forms of these foods not only tolerate their inclusion in the diet, but this exposure increases the rate of resolution 14-16-fold. We hypothesize that dietary exposure to sub-threshold levels of peanut in those with higher threshold levels of reactivity could lead to significant clinical improvement. Furthermore, studying the natural heterogeneity of PA is a valuable opportunity to elucidate mechanisms of disease. To study the clinical implications and mechanism of phenotypic heterogeneity in PA, we will conduct a randomized open feeding trial (CAFETERIA trial) to investigate a prototype approach where children with moderate PA (tolerating at least 100 mg of peanut) ingest a sub-threshold amount daily, with increasing levels tested every 3 months. The impact of dietary intervention will be tested at 1 and 2 years by oral food challenge. The CAFETERIA study will provide a rich biorepository of samples from highly phenotyped subjects. We anticipate screening 200-250 subjects, including low threshold, high threshold, and sensitized but not allergic, in order to enroll 98 subjects that meet the high threshold criteria for the CAFETERIA trial. We will obtain longitudinal samples from subjects randomized to dietary therapy or avoidance. We will comprehensively profile antibody responses by high-throughput epitope assay, peanut-specific T cell responses by flow cytometry, and whole blood activation by CyTOF to construct a detailed clinical-immune network of PA, and analyze the relationship between immune and clinical parameters. We will identify biomarkers and key causal drivers of PA by performing integrated network-based examination of peripheral blood transcriptomes from PA subjects, sampled before and after food challenge, and before and after dietary therapy. Successful completion of these aims will result in (1) a simple low-cost treatment option applicable to the majority of those with PA; (2) an identification of immune and molecular mechanisms of PA and response to dietary therapy; (3) peripheral blood biomarkers that will practically impact clinical care of PA; (4) the potential for personalized approaches to the treatment of PA; and (5) a tremendously rich resource of clinical, immune, and transcriptional data and analytic tools to be made publicly available to the research community.